In a host of processes involving solids, liquids, gases and mixtures thereof where the components and mixtures may be stationary, moving in batches or flowing continuously, there are needs for accurate, relatively inexpensive composition monitoring means and methods. Further, it is often desirable that these monitoring means be capable of working in-line with the processes to avoid process detours or by-passes for monitoring reasons. It is often desirable that the monitor be non-intrusive so as not to interfere with the processes being monitored and/or to prevent the monitoring means from being degraded by, for example, processes that are highly corrosive and/or erosive.
Typically such composition monitoring needs are related to the qualities and quantities of products being bought and sold, products being produced or of products being stored. Equally great are the needs for composition monitoring for purposes of process control, production efficiency and safety.
Among the processes having needs for composition monitoring, one particular process is oil production. Whether the oil production is on land or on offshore platforms or on the sea floor there is an unsatisfied need for the continuous monitoring of the quantities of oil, water and gas being produced. There are many different specific reasons for monitoring these three components, but their collective purpose is to optimize production.
Today, the three components of oil, water and gas can only be measured individually by means of separators. For individual well testing, smaller separators with less capacity than production separators are used. These are commonly known as test separators. In a given field, normally only one test separator is available and, therefore, the continuous monitoring of all wells simultaneously is not possible. Instead the wells are only tested at intervals, typically once or twice a month, but longer intervals are not uncommon. Such infrequent and unsatisfactory well testing is also due to the inherent slowness of the separation process and the necessary routine maintenance which includes the removal of deposits, such as sand. In addition there are elaborate and time consuming procedures for routing the production from the individual wells to the test separator.
Therefore, it is clear that there is a specific need for an inexpensive and practical composition monitor that can measure continuously the amounts of oil, water and gas being produced by each individual well in a production field or reservoir in order to know the performance and condition of each well. From these individual measurements, conclusions can be drawn about changes in the reservoir that might affect production rates and total recovery.
Another drawback of test separators is that on offshore platforms they constitute significant structural cost factors. Test separators typically weigh 15 to 20 tons, occupy considerable space and require crews for operation and maintenance. Weight, space and manning are major cost factors on platforms where, for example, the cost penalty per metric ton ranges anywhere from $200,000 to $600,000. Hence, on platforms there is a specific need for replacing the test separators with composition monitors that are light weight and do not require crews for operation. On offshore drilling rigs, an added incentive for replacing the test separators is that their functions are impaired by rig motions (roll and heave) including making them less safe to operate.
For drilling in general there is also a need for a compositional monitor that can measure, continuously, the oil, water, gas and solids content of the returning drilling mud. Among the reasons for such monitoring, the most important is to know if the reservoir is adding fluids to the returning mud and, if so, at what rate. Such reservoir production may signal a possible blow-out that can be prevented with early warning.
The existing means for detecting such influx from the reservoir are primitive and far from adequate. They consist, for example, of liquid level detectors with large tanks that are insensitive to small liquid volume changes.
A very costly composition monitoring task offshore is that of testing the production from subsea wellheads, particularly when the production from several wellheads is commingled into a single flow line to a receiving station. To avoid shutting down all wells but the one to be tested, an additional test line to the receiving station must be employed into which the individual well production is routed for testing at the receiving station. Installing an extra line is costly by itself, but routing of individual well production requires extra equipment, construction and controls that, particularly in a subsea environment, complicate and reduce total production reliability. Clearly, therefore, there is a great economic and practical need for composition monitoring means that can be an integral part of each subsea wellhead such that only the monitoring results need be transmitted to the receiving station by cable or acoustically.
Perhaps the ultimate need for well compositional monitoring means is for installation downhole at the reservoir production zone or zones. No such equipment exists today.
Another need of the petroleum industry for in-line continuous compositional monitoring means is the measurement of small amounts of water in oil for the purpose of custody transfer at points of delivery, at points along the pipeline, at receiving stations and in the further treatment/process and refining of oil products. At present, fiscal measurements are performed by taking frequent small product samples from which, usually by titration processes, the water contents are determined and recorded to give a statistically determined total water content. As can be expected, ignorance about the water content between samples results in disputes about the measurement procedures and the results between sellers and buyers.
In the petroleum industry, reservoir steam injection is often used to enhance and/or make possible the production of heavy oils, i.e. high viscosity oils that cannot flow freely and cannot be pumped. To recover such oils, high energy steam which readily permeates the reservoir is injected into it so that the thermal energy released when the gas condenses will heat the oil to lower its viscosity sufficiently so that it can be produced. During steam injection and after, all reservoir production wells are shut off. After a time, when it is thought that all water vapor has condensed in the reservoir, production begins and is continuous until steam injection is again required. The method here described is usually denoted the "huff and puff" method, but there are also steam "driven" fields where the injection of steam and the production are continuous. Obviously, from the above, it is economically desirable to monitor the quality of the injected steam. The higher the gas content, the higher the quality. Equally obvious is the economic importance of knowing whether or not the produced fluids contain uncondensed steam, which would represent unused energy.
Therefore, the petroleum industry and essentially all steam producers and users have need for continuous steam quality monitoring means. Another example of such producers and users is nuclear power plants.
Outside oil production there are many industries and businesses whose products and processes require close monitoring of composition, but which lack adequate continuous and/or batch monitoring means for doing so.
In the pulp and paper industry, there is a need for continuous monitoring of the water content of pulp liquors being pumped into combustion furnaces. If excessive water is present in the liquor, there is a danger that the furnace will explode. Because of a lack of suitably accurate, noninvasive monitoring means, some pulp and paper companies regularly budget for furnace explosions. An accurate monitoring means could be used to warn of excessively high water content in the liquor.
In the food processing industry, there is a also a need for a monitoring means that could rapidly determine the composition of processed and/or raw foods. Of particular concern is the water content. The dairy industry is a typical example. The fat and water content of milk and milk products must meet certain specifications to be sold in the marketplace, yet no adequate monitoring means for continuously measuring the fat and water content has been found. Consequently, dairy producers must put excessive milk fat into their products to ensure that they meet specifications. If an accurate, simple, continuous fat and water content monitoring means were available, the extra milk fat could be put towards the production of butter or ice cream.
Fuel transportation and distribution systems have need for an accurate, continuous means for monitoring the water content of the fuels. For example, there is a need to measure the water content of jet fuels when they are being pumped into aircraft. A small percentage of water is added to jet fuels to improve combustion efficiency, but if excessive water is present, serious problems can occur during operation, including engine failure.
Within the petrochemical and chemical industries, there are a host of composition monitoring needs where the liquids involved may not be water. Examples of such process liquids are plastic resins, polymers, alcohols, acids, and organic solvents. In each case, there exists a need for a simple, continuous, rugged, chemically inert, and inexpensive monitoring means which can continuously measure the composition of mixtures of these chemicals as they are being processed and purified.
For many of the composition monitoring examples cited, no technology is currently available to perform the process monitoring tasks. It is an object of this invention to describe a monitoring means and apparatus which satisfies the central composition monitoring requirements that are common to these and many other applications like them. The common requirements are that a monitoring means be:
1) in-line,
2) measure continuously (i.e. have a short measurement cycle time),
3) able to withstand
Difficult process conditions, PA1 High internal temperatures and pressures PA1 Corrosive process components PA1 Abrasive components PA1 Viscous liquids,
4) noninvasive,
5) accurate,
6) insensitive to geometry outside test section
7) reliable,
8) relatively inexpensive,
9) and tough enough to withstand industrial environments.